The invention relates a fluid system phenomena known as xe2x80x9cwaterhammerxe2x80x9d and more particularly to apparatus for suppressing waterhammer in operating water systems such as municipal water systems and process and utility service water systems in nuclear power and other industrial plants.
Surge suppressors are commonly used in water systems to absorb hydraulic transients causing waterhammer, which may occur when pumps startup or shut down or when valves rapidly open or close. See, in this regard, U.S. Pat. No. 5,218,987 to Heil, which discloses a surge suppressor for protecting fire hydrant systems. Such surge suppressors are essentially surge vessels (which may be standpipes) hydraulically connected with the water systems for absorbing the forces of hydraulic transients. The surge vessels comprise water filled portions which may or may not be separated from gas filled portions by flexible, substantially watertight membranes or bladders. For those suppressors using bladders, the hydraulic transients in the water in the systems cause the water in the surge vessels to act on the membranes and compress the gas (which may be compressed air) behind the membranes and thereby absorb the energy. See, also, U.S. Pat. No. 5,303,843 to Zinc et al., which illustrates the use energy absorbing materials disposed in compartments isolated by rupture disks from fluid containing compartments in railroad cars to absorb the energy generated in the fluid in the course of an accident.
Operators of water systems are concerned about the reliability of flexible membranes and bladders in water systems, which must function over a wide range of conditions. One concern for those suppressors that do not use bladders is that significant amounts of the gas contained in the surge suppressors may dissolve into the water over time and the surge suppressors might not then retain their capacity to absorb the hydraulic transients. Another concern is that the gas originally in the surge vessel may dissolve into the water and then may contribute to cavitation or have other adverse affects.
It is an object of the present invention to suppress water hammer in water systems without requiring the use of flexible membranes or bladders to separate the water and gas in surge suppressors. It is a further object to reduce the amount of gas in surge suppressors available to dissolve into the water.
With these objects in view, the present invention resides in apparatus for suppressing water hammer in a water system. The apparatus comprises a surge vessel having a permanently open nozzle for hydraulically connecting with the water system, a cellular polymer in the surge vessel and a water permeable screen spaced from the nozzle separating the nozzle and the cellular polymer and retaining the cellular polymer in the surge vessel. Preferably, the polymer is a plastic foam (or cellular plastic) comprised of polyethylene, polyurethane or polystyrene. In one embodiment of the present invention, separate cellular polymer particles are contained in netting.
Advantageously, a hydraulic transient in a water system sufficient to generate a waterhammer condition will at least partially crush the cellular polymer, which will absorb the energy in the water. Also, the polymers (and entrapped gases therein) will occupy much of the volume of the surge vessels not occupied by the water so that less gas is available to dissolve into the water.